Method and Apparatus for Controlling Charging in a Communication Network

ABSTRACT

A method and apparatus for controlling a present service charging session for charging service usage in a communication network. The method comprises receiving a first request for grant of a reservation service unit quota from a charging client, the first request including at least data identifying an account to charge for the service usage. A first granted service unit quota for the first request is determined and a first carry-over service units quota from a previous service charging session associated with the identified account is accessed. A first reservation service unit quota is determined by deducting the first carry-over service units quota from the first granted service unit quota. According to the method it is reserved for the first reservation service unit quota from the account and the first granted service unit quota is sent to the charging client. Further, a clearing request is received from the charging client including data enabling a first used amount of service units to be determined. An outstanding service unit quota is determined by deducting the first carry-over service unit quota from the first used amount of service unit and the outstanding service unit quota from the account is deducting for. An advantage is that for example mechanisms for reducing resource usage in the communication network, such as for example Quota-Holding-Time defined in 3GPP 32.299, may be used and still get a correct charging of used services thereby avoiding premature denial of service when the account is extinct.

FIELD OF INVENTION

The present invention relates to controlling charging in a communicationnetwork and more particularly to a method and apparatus for controllinga present service charging session for charging service usage.

BACKGROUND

In telecommunication networks charging for usage is usually done forevery started period, called charging interval. The charging intervalcan be from one second to several minutes for calls and ranging frombytes to megabytes for data. It is common that a subscriber is chargedfor every started minutes of a call. For example if the subscriber talksfor one minute and one second the subscriber will have to pay for twofull minutes.

To be able to handle data usage there is a need to define when the usagehas stopped since this is not as clear as detecting an on-hook for avoice call. To solve this the 3:rd Generation Partnership Project (3GPP)standardization has introduced a parameter that can be used to identifythat traffic (that consumes a granted quota) has stopped. This parameteris called Quota-Holding-Time (QHT) and is specified by 3GPP TS 32.299V10.1.0 (2011-03).

The parameter is used on the Ro reference point in the 3GPP chargingarchitecture. The Ro reference point is for example used for charging ofdata bearer traffic and different IP Multimedia Subsystem (IMS)services. The Ro reference point is between the charging client andOnline Charging System (OCS).

If no traffic associated with a consumption quota granted to a chargingclient by a charging server is observed for the duration of the QHT, thecharging client understands that the traffic has stopped and theconsumption quota is returned to the server.

By using Quota-Holding-Time the telecommunications network operator hasthe possibility to not have reservations allocated on the subscribersaccount for services that is not currently used. Normally there is onecharging session for example for one Packet Data Protocol (PDP) context.If the subscriber is using several services during the lifetime of thecharging session there can be several reservations on the subscriberaccount.

If Quota-Holding-Time, or a similar timer set locally in the chargingclient, is not used this will result in a large part of the subscriber'sbalance of funds being blocked for those reservations. As a result,services may be denied because of a virtual lack of available funds,although funds are available but distributed and allocated asconsumption quota for different charging sessions.

For voice calls the duration is usually relatively easy to estimate andin most cases optimize the calls so that the time is utilized optimally.This is to some extent also true for data. The issue here is that theuser normally does not have full control over when a charging session isconsidered started or stopped. A solution to this today is to have itbased per bill period (e.g. month) but this is difficult when having anonline charged subscriber (e.g. prepaid) since they expect to have anupdated and correct statement immediately.

However, the use of Quota-Holding-Time or similar methods createsanother problem. Consider a Quota-Holding-Time set to five minutes. In apossible scenario the subscriber is web browsing and a page isdownloaded. The subscriber may read the page for a duration that islonger than five minutes. Due to the QHT timer the service chargingsession, where a service charging session is defined as the session forcharging the service usage until the service usage is identified asstopped using for example Multiple Services Credit Control (MSCC) asspecified by the Internet Engineering Task Force (IETF) RFC 4006 as atype of sub-sessions, is terminated.

At the termination the used units are deducted and any unused quota isreturned to subscribers account. The deduction is rounded upwards to thecharging interval i.e. the granularity used for charging of the usedunits. The charging interval may for example be 1 kilobyte and the usedvolume is thereby charged for every started kilobyte.

The subscriber may then select to click on next link and a new web pageis downloaded and a new service charging session started, and so on foreach subsequent page. Each time the service charging session isterminated the service usage is rounded upwards to the charginginterval. When summarizing the total usage the subscriber may therebyhave paid significantly more than would the service charging sessionbeen up all the time.

The cause to the problem is that service charging sessions are startedand terminated several times during a charging session. The subscriberexperience the web surfing as one usage session but the OCS is handlingit as several smaller service charging sessions.

For a voice call the rounding to the next charging interval is made atthe end of the call when the subscriber decides to terminate the call. Asimilar behavior is wanted for a data session in that rounding shouldnot be done several times during a data session just because ofsignaling optimization and instead leading to an overcharge.

Also, the charging interval must be configurable based on the operator'sbusiness requirements, in the same way the operator in many casesdecides to have a charging interval of one minute for voice. For examplethe operator must be able to configure for example charging interval to50 KB for roaming data (this is a normal interval for the roaming case).The real usage is normally measured in higher granularity (i.e. moredetailed) than the charging interval which gives the affect as describedin above example.

As has been illustrated above, QHT or similar timers are used to end aservice charging session at inactivity and to return the allocatedreservation to be usable for other sessions as to avoid a virtual lackof funds and the resulting service denial. Inactivity may, as has beendescribe, be erroneously deduced because of the user still e.g. readinga web page but may also result from the user terminal losing itsconnection due to e.g. out of radio coverage of a mobile device.

As has also been shown such ending of a service charging session maycause excess charging of the user causing a premature extinction offunds thereby also resulting in denial of service.

A problem is thus that excess charging of a subscriber's accounts due tounintentional service charging session interruptions causes prematuredenial of service when the account is extinct.

SUMMARY OF INVENTION

An object of the invention is to provide a method and apparatus forcontrolling a present service charging session for charging serviceusage in a communication network mitigating the problem that excesscharging of a subscriber's accounts due to unintentional servicecharging session interruptions causes premature denial of service whenthe account is extinct.

One aspect of the invention relates a method performed by a chargingcontrol node for controlling a present service charging session forcharging service usage in a communication network. The method comprisesreceiving a first request for grant of a reservation service unit quotafrom a charging client, the first request including at least dataidentifying an account to charge for the service usage. A first grantedservice unit quota for the first request is determined and a firstcarry-over service units quota from a previous service charging sessionassociated with the identified account is accessed. A first reservationservice unit quota is determined by deducting the first carry-overservice units quota from the first granted service unit quota. Accordingto the method it is reserved for the first reservation service unitquota from the account and the first granted service unit quota is sentto the charging client. Further, a clearing request is received from thecharging client including data enabling a first used amount of serviceunits to be determined. An outstanding service unit quota is determinedby deducting the first carry-over service unit quota from the first usedamount of service unit and the outstanding service unit quota from theaccount is deducting for.

It is an advantage that for example mechanisms for reducing resourceusage in the communication network, such as for exampleQuota-Holding-Time defined in 3GPP 32.299, may be used and still get acorrect charging of used services thereby avoiding premature denial ofservice when the account is extinct.

Another aspect of the invention relates to a charging control node forcontrolling a present service charging session for charging serviceusage in a communication network comprising an interface unit adaptingthe charging control node for receiving a first request for grant of areservation service unit quota from a charging client, the first requestincluding at least data identifying an account to charge for the serviceusage. The charging control node also comprises a determination unitadapting the charging control node for determining a first grantedservice unit quota for the first request; accessing a first carry-overservice unit quota from a previous service charging session associatedwith the identified account; determining a first reservation serviceunit quota by deducting the first carry-over service unit quota from thefirst granted service unit quota; reserving for the first reservationservice unit quota from the account. The interface unit is furtheradapting the charging control node for sending the first granted serviceunit quota to the charging client and receiving a clearing request fromthe charging client including data enabling a first used amount ofservice units to be determined. The determination unit is furtheradapting the charging control node for determining an outstandingservice unit quota by deducting the first carry-over service unit quotafrom the first used amount of service unit and deducting for theoutstanding service unit quota from the account.

A further aspect of the invention relates to a charging controlapparatus having a processor and a memory. The memory is storinginstructions that, when executed by the processor, cause the apparatusto receive a first request for grant of a reservation service unit quotafrom a charging client, the first request message including at leastdata identifying an account to charge for the service usage; determine afirst granted service unit quota for the first request; access a firstcarry-over service units quota from a previous service charging sessionassociated with the identified account; determine a first reservationservice unit quota by deducting the first carry-over service units quotafrom the first granted service unit quota; reserve for the firstreservation service unit quota from the account; send the first grantedservice unit quota to the charging client; receive a clearing requestfrom the charging client including data enabling a first used amount ofservice units to be determined; determine an outstanding service unitquota by deducting the first carry-over service units quota from thefirst used amount of service unit and deduct for the outstanding serviceunit quota from the account.

Embodiments of the invention will now be described in more detail withreference to the enclosed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example online chargingarchitecture wherein the invention is useful.

FIG. 2 is a block diagram showing session charging according to anexemplary embodiment of the invention.

FIG. 3 is a message sequence chart showing session charging with unitreservation according to an exemplary embodiment of the invention.

FIG. 4 is a message sequence chart showing a method for controllingservice charging session for charging service usage according to a firstexemplary embodiment of the invention.

FIG. 5 is a message sequence chart showing a method for controllingservice charging session for charging service usage according to asecond exemplary embodiment of the invention.

FIG. 6 is a flow chart showing a method for controlling chargingaccording to an exemplary embodiment of the invention.

FIG. 7 is a block diagram showing an exemplary computing device forimplementing a charging control node for controlling a present servicecharging session for charging service usage in a communication networkin the form of computing system environment 800.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of the exemplary embodiments refersto the accompanying drawings. The same reference numbers in differentdrawings identify the same or similar elements. Also, the followingdetailed description does not limit the invention. Instead, the scope ofthe invention is defined by the appended claims.

FIG. 1 is a block diagram showing an example online chargingarchitecture wherein the invention is useful.

A Communication network 100 provides functions that implement onlinecharging mechanisms as charging clients in charging trigger functions(CTF) of Network Elements (NE) on the core network 105—e.g. EvolvedPacket Core (EPC), subsystem 110—e.g. IP Multimedia Subsystem (IMS) andservice 115—e.g. Multimedia Messaging System (MMS) levels. In order tosupport these charging mechanisms, the network performs real-timemonitoring of required network resource usage on the above three levelsin order to detect relevant chargeable events.

In online charging, a subscriber account holding subscriber related dataas balance level of monetary funds, services subscribed to etc, locatedin an Online Charging System (OCS) 120, is queried prior to grantingpermission to use the requested network resource(s).

Typical examples of network resource usage are a voice call of certainduration, the transport of a certain volume of data, or the submissionof a multimedia message of a certain size. The network resource usagerequests may be initiated by a User Equipment UE (not shown) or by thenetwork 100.

Online charging is a process where charging information for networkresource usage is collected concurrently with that resource usage.However, authorization for the network resource usage is obtained by thenetwork prior to the actual resource usage occurs. This authorization isgranted by the OCS upon request from the network.

When receiving a network resource usage request the Charging TriggerFunction (CTF) 125 of the network assembles the relevant charginginformation and generates a charging event towards an Online ChargingFunction (OCF) 130 of the OCS in real-time. The OCS then returns anappropriate resource usage authorization. The resource usageauthorization may be limited in scope (e.g. service unit quota of volumeof data or duration), therefore the authorization may have to be renewedfrom time to time as long as the network resource usage persists.

The charging event is forwarded to the OCF in order to obtainauthorization including a service usage quota for the chargeableevent/network resource usage requested by the UE or network. The CTF isalso able to track the availability of resource usage permission (“quotasupervision”) during the network resource usage.

Online charging in the Circuit Switched (CS) and Packet Switched (PS)domains may also be performed using the Customized Applications forMobile networks Enhanced Logic (CAMEL) Application Part (CAP) protocoland the CAP reference point from the Mobile Switching Centre (MSC) andServing GPRS Support Node (SGSN), respectively, to the OCF. Othernetwork elements may employ an Ro reference point 235 for onlinecharging using Diameter Credit Control application. Similarly, Woreference point may be employed for Wireless Local Area Network (WLAN),Gx and Gy reference points may be employed for Policy and ChargingControl (PCC) according to the 3rd Generation Partnership Project 3GPPas described in TS 23.203 V10.2.1 (2011-01).

The Ro reference point from the CTF 125 to the OCF 130 is intended forthe transport of charging events for online charging. A Ga 140 referencepoint is the interface between the OCF and a Charging Gateway Function(CGF) 145 which connects a Billing Domain (BD) 150 over a Bo 155reference point.

The Ro reference point supports interaction between a Charging TriggerFunction and an Online Charging Function. The following information mayflow across this reference point:

-   -   Charging events for online charging from the CTF to the OCF.    -   Receive acknowledgements for these charging events from the OCF        to the CTF. The acknowledgement grants or rejects the network        resource usage requested in the charging event, according to the        decision taken by the OCS.

The CAP reference point provides similar functionality for onlinecharging as Ro, however, it is based on CAMEL techniques.

Different mappings of the online charging functions, CTF, OCF and CGF,onto physical implementations are possible.

Each CTF may have an OCF address list to which it can send its chargingevents and/or charging requests.

FIG. 2 is a block diagram showing session charging according to anexemplary embodiment of the invention.

A charging session is started in the OCF at t1 as a result of a requestfor a reservation service unit quota (RSUQ) from a CTF, for example in aPolicy and Charging Enforcement Function (PCEF), following for examplethe setup of a data bearer at the client. At this point a chargingsession state is created. The charging session state is used as acontainer for any future surviving session states. This is to supportparallel charging sessions so that one service session in one chargingsession does not affect a service session in another charging session.In case sub-sessions, for example MSCC as described by IETF RFC 4006 isused, also a service charging session is started as a result of thereservation request from the CTF. At time t2 the OCF responds with agranted reservation service unit quota and optionally a quota holdingtime (QHT), e.g. as defined by 3GPP TS 32.299 V10.1.0 (2011-03), to theCTF and the service usage may be started at the client. At time t3 theservice charging session is terminated because QHT times out at the CTFfollowing a QHT timeout following ceased service usage. The number ofused units and the number of charged units for the service session, or aCarry-over amount of Service Units (CSU) computed from these, are storedin the surviving session state. At time t4 a new service usage isstarted for the same service which triggers a new request for RSUQ fromthe CTF and establishment of a new service charging session at the OCS.The number of used units' and the number of charged units' values arefetched from the session state. The amount of units used in the newreservation is calculated in the following formula:

Units to be granted in reservation=new requested number ofunits−(charged units−used units).

The granted reservation service unit quota is returned to the CTF andservice usage is allowed to continue at time t5. At time t6 the servicesession is terminated because data bearer is terminated and the usedservice units is reported to the OCS. The amount of service units todeduct from the account is calculated in the following formula:

Units to be deducted for =new used number of units−(charged units−usedunits).

In case usage of carry-over units are not allowed between chargingsessions the surviving session state may now be deleted. It isoptionally possible to reset the surviving session state with someinterval to handle the case when subscriber is always connected, forexample nightly, monthly or synchronized with billing cycle. It is alsopossible to configure for how long the service can be unused before thereset is done.

FIG. 3 is a message sequence chart showing session charging with unitreservation according to an exemplary embodiment of the invention.

According to 3GPP TS 32.299 on-line credit control can be structured asusing two basic logical operations: Debit Units and Reserve Units.

Debit Units Request is sent from CTF to OCF. After receiving a servicerequest from the subscriber, the CTF sends a Debit Units Request to theOCF. The CTF may either specify a service identifier (centralized unitdetermination) or the number of units requested (decentralized unitdetermination). For refund purpose, the CTF sends a Debit Units Requestto the OCF as well.

Debit Units Response is sent from OCF to CTF. The OCF replies with aDebit Units Response, which informs the CTF of the number of unitsgranted as a result of the Debit Units Request. This includes the casewhere the number of units granted indicates the permission to render therequested service. For refund purpose, the OCF replies with a DebitUnits Response.

Reserve Units Request is sent from CTF to OCF and is a request toreserve a number of units for the service to be provided by a CTF. Incase of centralized unit determination, the CTF specifies a serviceidentifier in the Reserve Unit Request, and the OCF determines thenumber of units requested. In case of decentralized unit determination,the number of units requested is specified by the CTF.

Reserve Units Response is sent from OCF to CTF. The response from theOCF informs the CTF of the number of units that were reserved for as aresult of the “Reserve Units Request”.

Session charging with unit reservation may use the Session Based CreditControl procedure specified in RFC 4006 by the IETF. In session chargingwith unit reservation, when the “Debit Units” and “Reserve Units”operations are both needed, they may be combined in one message.

The consumed units are deducted from the subscriber's account afterservice delivery. Thus, the reserved and consumed units are notnecessarily the same. Using this operation, it is also possible for theCTF to modify the current reservation, including the return ofpreviously reserved units.

The corresponding IETF RFC 4006 Diameter Credit Control Application(DCCA) messages for the Debit/Reserve Unit Request operation isCredit-Control-Request (CCR) and for the Debit/Reserve Unit Responseoperation is Credit-Control-Answer (CCA).

DCCA specifies an approach based on a series of “interrogations”:

-   -   Initial interrogation.    -   Zero, one or more interim (also called intermediate)        interrogations.    -   Final interrogation.

In addition to a series of interrogations, also a one time event(interrogation) can be used e.g. in the case when service execution isalways successful.

All of these interrogations use CCR and CCA messages. The CCR for the“interim interrogation” and “final interrogation” reports the actualnumber of “units” that were used, from what was previously reserved for.This determines the actual amount debited from the subscriber's account.

In step 305 the CTF 125 of a network element, for example a PCEFreceives a session initiation request. The session initiation may bedone either by a user equipment or another network element.

In order to perform Reserve Units operation for a number of units(monetary or non-monetary units), the CTF sends a CCR with CreditControl CC-Request-Type set to INITIAL_REQUEST to the OCF 130 of an OCSin step 310. As a result of the CCR from the charging client a chargingsession is started. If known, the network element may includeRequested-Service-Unit (RSU) as monetary- or non monetary units (e.g.service units, data volume, time and events) in the request message.

At this point a charging session state is created. The charging sessionstate is used as a container for any future surviving session states.This is done to support parallel charging sessions but also so that oneservice charging session in one charging session does not affect aservice charging session in the same charging session.

A service charging session may be implemented using Multiple ServicesCredit Control (MSCC). MSCC is specified by the IETF RFC 4006 as a typeof sub-sessions. MSCC shall not be mixed up with the sub-sessions of RFC4006 as specified in chapter 5 of RFC 4006, which may also be used.

The CCR may in accordance with RFC 4006 paragraph 8.16 include a MSCCAttribute Value Pair (AVP) which contains the AVPs related to theindependent credit-control of multiple services. Each instance of anMSCC AVP in the CCR carries units related to one or more services orrelated to a single rating group.

The Multiple-Services-Control AVP may include: Granted-Service-Unit;Requested-Service-Unit; Used-Service-Unit; Tariff-Change-Usage;Service-Identifier; Rating-Group; G-S-U-Pool-Reference; Validity-Time;Result-Code and Final-Unit-Indication.

Service charging session is the session for charging the service untilthe service is identified as stopped.

When MSCC is used the service charging session is started as the resultof a CCR request including an MSCC AVP from the charging client, forexample PCEF, which contains a request for service units. A survivingsession state is created for the service charging session at the OCF.

In step 315 a granted service unit quota is determined. If the servicecost information is not received by the OCS, the OCS determines theprice of the desired service according to service specific informationreceived by issuing a rating request to a rating function of the OCS. Ifthe credit balance is sufficient, the OCS reserves the amountcorresponding to the service units quota from the subscriber's account.If the cost of the service is included in the request, the OCS maydirectly reserves the specified monetary, it may also rate the event foradd-on charges or discounts.

Once the reservation has been made, the OCS returns CCA message withCC-Request-Type set to INITIAL_REQUEST to the CTF of the network elementin step 320 in order to authorize the service execution.Granted-Service-Unit (GSU) and possibly Cost-Information indicating thecost of the service and Remaining-Balance are included in the CCAmessage. The OCS may return a Validity-Time (VT) with value field set toa non-zero value. The OCS may indicate in a Low-Balance-Indication thatthe subscriber account balance has fallen below a predefined thresholdof this account. If MSCC is used the response also includes the MSCCresponse AVPs including quotas per service charging session. AQuota-Holding-Time idle timeout as specified by 3GPP TS 32.299 V10.10.0(2011-03) paragraph 6.5.1.1 may further be included with the CCA. TheOCS may specify an idle timeout associated with a granted quota usingthe Quota-Holding-Time AVP. If no traffic associated with the quota isobserved for this time, the charging client/CTF determines the trafficas stopped and the quota is returned to the server

Thus, the service charging session is terminated because QHT times out.If the QHT is not provided by the CCA messages a local quota holdingtime can employed by the charging client.

Content/service delivery starts in step 325 and the reserved units areconcurrently controlled by the CTF.

During session delivery, in order to perform Debit Units and subsequentReserve Units operations, the network element sends a CCR withCC-Request-Type set to UPDATE_REQUEST, to report the Used-Service-Unit(USU) and request additional service units using an RSU, respectively,in step 330. The CCR message with CC-Request-Type set to UPDATE_REQUESTis sent by the CTF of the network element between a INITIAL_REQUEST andTERMINATION_REQUEST either on request of the credit control applicationwithin the validity time or if the validity time is elapsed. If known,the network element may include Requested-Service-Unit as monetary ornon monetary units in the request message. USU is complemented in theCCR message to deduct units from both the subscriber's account and thereserved units, respectively.

If MSCC is used, a CCR may include 1 . . . n MSCC AVPs. The MSCC AVP mayfurther include a Reporting-Reason AVP indicating the QHT has timed outfor a MSCC granted in step 320. Such MSCC AVP can be included in a CCRincluding for example RSU as previously described but a CCA may also beused only in order to convey an MSCC terminating a service chargingsession due to QHT time out.

In step 335 an USU is first analyzed and the corresponding amount isdeducted from the account. If the service cost information is notreceived by the OCS, the OCS determines the price of the desired serviceaccording to the service specific information received by issuing arating request to the rating function. If the credit balance issufficient, the OCS reserves the amount from the subscriber's account.If the cost of the service is included in the request, the OCS directlyreserves the specified monetary amount. The OCS may also rate the eventfor add-on charges or discounts.

An MSCC termination can be done due to the Quota-Holding-Time idletimeout. If no traffic associated with the quota is observed for thistime, the charging client/CTF determines the traffic as stopped and thequota is returned to the server as implied by an USU within the MSCCAVP.

Thus, the service charging session is terminated because QHT times out.

Although an MSCC is terminated due to a QHT time out the charging amountdeducted from the account should not be affected by the optimizationdone by using the Quota-Holding-Time parameter. For example a subscriberis charged 1.50

for every started megabyte (MB) of data transmission. The user thentransmits 1.5 MB which would result in a remainder of 0.5 MB. The ratedcharge would be for the 1:st MB is 1.50+cost for the 0.5 MB i.e. 1.50gives a total cost of 3

. Taking 3/1.50 and this gives 2 MB and the remainder (or unused quota)is then 2−1.5 which is 0.5 MB. This remainder value, or the used unitsUSU as well as the charged units for the service session are stored inthe surviving session state for usage by later charging or servicecharging sessions.

Once the deduction and reservation have been made, the OCS returnsCredit-Control-Answer message with CC-Request-Type set to UPDATE_REQUESTto the network element in step 340, in order to allow thecontent/service delivery to continue, new Granted-Service-Unit (GSU),possibly Cost-Information (CI) indicating the cumulative cost of theservice, Remaining-Balance, and MSCC, are included in the CreditControl-Answer message. The OCS may include in the CCA message aFinal-Unit-Indication (FUI) to indicate the final granted units. The OCSmay indicate in a Low-Balance-Indication that the subscriber accountbalance has fallen below a predefined threshold of this account. Also aQHT AVP may be included.

Session delivery continues and the reserved units are concurrentlycontrolled by the CTF in step 345.

The session is terminated at the CTF of the network element in step 350.

The network element sends CCR with CC-Request-Type set toTERMINATION_REQUEST to terminate the active credit control session andreport the used units in step 355. If used, also MSCC is included.

The termination can be done due to a Quota-Holding-Time idle timeout. Ifno traffic associated with the quota is observed for this time, thecharging client determines the traffic as stopped and the quota isreturned to the server as implied by the USU. Thus, the charging sessionis terminated because QHT times out.

The OCS deducts for the used units from the account. Unused reservedunits are released, if applicable, in step 360. Similarly to terminationof an MSCC in step 330, a remainder or the used units USU as well as theunits charged for the service session are stored in the survivingsession state for usage by subsequent charging sessions.

During the charging session, further CCR UPDATE_REQUEST as in step 330may take place initiating new MSCC service charging sessions. A singleCCR UPDATE_REQUEST may terminate 1 . . . N MSCCs and initiate 1 . . . Nnew MSCCs. The remainder, or used units' and charged units' values arefetched from the surviving session state. The amount of units used inthe new reservation is calculated as:

Units to be used in reservation=new requested units−(charged units−usedunits)

Once an MSCC service charging session is terminated, for example becausethe data bearer is terminated and the charging session therebyterminated, the amount of units used in the deduction is calculated inthe following formula:

Units to be used in deduction=new used units−(charged units−used units)

The OCS acknowledges the reception of the CCR message by sending CCAmessage with CC-Request-Type indicating TERMINATION_REQUEST (possiblyCost-Information indicating the cumulative cost of the service andRemaining-Balance are included in the Credit-Control-Answer message) instep 365.

FIG. 4 is a message sequence chart showing a method for controllingservice charging session for charging service usage according to a firstexemplary embodiment of the invention.

A service charging session is an OCS session which takes place within acharging session. The charging service session corresponds to a trafficflow. This may correspond to the service usage using a data connectionplus an associated QHT (where applicable). The charging service sessionmay also correspond to e.g. a voice call where the charging servicesession incorporates the charging session. For data traffic a chargingsession in the OCS corresponds to a data bearer, e.g. a PDP Context, atthe client. Thus, for a voice call a service charging session wouldequal a charging session and for a data connection the service usagewould correspond to the data bearer. Service usage is the traffic flow,i.e. service usage, in the charging client, e.g. a PCEF

The charging session is started as a result of a request from thecharging client, for example PCEF. At this point a charging sessionstate is created. The charging session state is used as a container forany future surviving session states. This to support parallel chargingsessions but also so that one service charging session in one chargingsession does not affect a service charging session in the same chargingsession.

In one possible implementing the charging protocol used forcommunication between the CTF and the OCS is the IETF RFC 4006. In suchcase the mechanisms used for the service charging session may be anInternet Engineering Task Force Multiple Services Credit Controlsub-session. A useful extension of RFC 4006 is 3GPP 32.299 V10.1.0(2011-03) introducing for example a QHT AVP.

The service charging session is started as a result of a request fromthe charging client, for example PCEF, in step 405 which contains arequest for grant of Reservation Service Unit Quota (RSUQ). The requestincludes data identifying an account to charge for the service usage.The account may belong to the subscriber involved in the serviceprovided by the client or an account of another subscriber determined bythe OCS. A surviving session state is created.

Step 415 together with step 420 describes in further detail the chargingcontrol carried on in step 315 and 335 of FIG. 3. In step 415 the RSUQis determined. The granted RSUQ can be determined from the receivedrequest (decentralized unit determination) or be determined by the OCF(centralized unit determination) and this RSUQ is then reserved for fromthe account in step 420. Normally a monetary value is reserved from theaccount by rating the RSUQ.

A reservation response is returned from the OCF to the CTF in step 425.The session is then ongoing and the CTF is supervising the session instep 435 so that the granted RSUQ is not exceeded.

The service session may be terminated because the units of a finalreservation emptying the account have been consumed. The session mayalso be terminated because the user has ended its service usage, e.g.made an on-hook during a voice call. In this scenario, however, it isassumed that in step 440 a termination request including the used numberof service units is received from the CTF because a QHT in the CTF hasexpired due to an idle period.

In step 445 the number of units to charge for is determined. For examplea subscriber is charged 1.50

/minute for every started minute. The user then talks for 1.5 minutesresulting in that 2 minutes should be deducted for from the account. The2 minutes are rated in step 450 resulting in a cost of 3

which is deducted from the account.

To make the charging of the usage not affected by the optimization doneby using the Quota-Holding-Time parameter a CSU quota is determined instep 460 by determining the difference between units charged for anddeducted in step 450, and the units actually used. In the presentexample the charged deduction in step 450 resulted in a CSU quota of 0.5minutes, i.e. the remainder between the 2 minutes charged for and the1.5 minute consumed by the user.

Step 460 may also include determining a rule for accessing the CSUquota. In one example rule, the rule includes a timer value so thataccess to the CSU quota is only to be allowed if the timer is unexpired.

To allow for reducing the excess charging due to the difference betweenused units and units charged for the determined CSU quota are storedwith the surviving session state. The CSU quota may also be preserved bystoring the used units and charged for units such that the CSU's may becomputed. Thus, in step 465 data is stored in the surviving sessionstate in association with the account such that the CSU quota based ondifference between the charged amount of service units and the usedamount of service units can be determined. Also, the determined rule foraccessing the CSU quota may be stored in association with the account.

The CSU's may have a rule associated with them so that the units may bereserved for certain usage or services, for example that CSU's frominternational calls cannot be used for national calls etc.

In an optional implementation it is possible to reset the survivingsession state with some interval to handle the case when subscriber isalways connected, for example each midnight or every hour. It ispossible to configure for how long the service can be unused before thereset is done. To cater for this a timer is introduced, calledStateTimer. The StateTimer is started to handle when the values insurviving session state should be cleared. The end time of the timercould thus be set to either duration (e.g. in one hour) or specifiedtime (e.g. midnight). In step 470 such StateTimer times out and valuesin the surviving session state are cleared.

FIG. 5 is a message sequence chart showing a method for controllingservice charging session for charging service usage according to asecond exemplary embodiment of the invention.

FIG. 5 shows scenarios applicable for three different scenarios. Inalternative I a first interrogation is followed by an intermediateinterrogation wherein steps 515-525 corresponds to step 315 and steps550-570 corresponds to step 335. In alternative II an intermediateinterrogation is followed by a final interrogation wherein steps 515-525corresponds to step 335 and steps 550-570 corresponds to step 360. Inalternative III a first interrogation is followed by a finalinterrogation wherein steps 515-525 corresponds to step 315 and steps550-570 corresponds to step 360.

In step 505 a request for grant of a RSUQ from a charging client isreceived. The request message includes data identifying an account tocharge for the service usage as well as other session relatedparameters. The account may belong to the subscriber involved in theservice provided by the client or an account of another subscriberdetermined by the OCS. This does not necessarily be the same account asdetermined in step 505 of FIG. 5.

A granted service unit quota for the request is determined in step 515.The granted service unit quota can be determined from the receivedrequest (decentralized unit determination) or it can be determined bythe OCS (centralized unit determination).

A CSU quota is accessed from a previous service charging session stateor charging session state associated with the identified account in step517. The used units' and the charged units' values are fetched from thesession state. If access rules are associated with the CSU's a check ismade for such rules and the CSU quota is only accessed if allowed bysuch rules. In one example the rule includes a timer and the CSU quotais only accessed if the timer is unexpired.

In step 520 an RSUQ is determined by deducting the accessed CSU quotafrom the granted service unit quota. The reservation may be smaller thanthe granted service unit quota because the CSU quota has been deducted(i.e. charged for) earlier and need not to be reserved for. The amountof units used in the new reservation is calculated in the followingformula:

Units to be used in reservation=new requested units−(charged units−usedunits)

Reservation for the RSUQ from the account is performed in step 525.Normally a monetary value calculated by rating the RSUQ is reserved fromthe account.

In step 530 the granted service unit quota is sent to the chargingclient. The sending of the granted service unit quota may includesending also a quota holding time parameter.

The session is ongoing and the CTF is supervising the consumption ofgranted units in step 535.

In step 540 a clearing request is received from the charging clientincluding data enabling a first used amount of service units to bedetermined. The clearing request may be received following a quotaholding time expiry at the CTF when service usage has ended. Serviceusage may comprise a data service usage including any of a data bearer,IP bearer, IP flow, service data flow, or a voice call. Thus, theclearing request may constitute for example a final interrogation afterthe service usage is released. The clearing request may also constitutean intermediate interrogation wherein a new quota is requested. Theclearing request may also constitute an intermediate interrogationterminating one or several service charging sessions eg. MSCCs. Onecause of a final interrogation terminating the service session is may bethat the data bearer is terminated.

The amount of units used in the deduction is calculated in step 550. AnOutstanding Service Unit (OSU) quota is determined by deducting the CSUquota from the used amount of service units. The following formula isuseful:

OSU quota to be used in deduction=new used units−(charged units−usedunits)

The OSU quota is deducted for from the account in step 560.

In step 565 a CSU quota based on the difference between the OSU quotaand the amount of service units deducted for is determined. The CSUquota is stored in association with the account in step 570. Generally,it is determined and stored data in association with the account suchthat the CSU quota based on difference between the OSU quota and theamount of service units deducted for can be determined.

If the use of CSU's is not allowed between charging sessions thesurviving session state may now be cleared or deleted.

A present service charging session using a CSU quota and a previousservice charging session creating a CSU quota may relate to the samecharging session or they may related to separate charging sessions.

FIG. 6 is a flow chart showing a method for controlling chargingaccording to an exemplary embodiment of the invention.

At the end of a normal session the following steps are performed:

In step 601 the session is considered ended and the used quotas arereceived. In step 602 it is checked if there is any applicable remainderquota and these are deducted these from the used quotas. Then, in step603 it is calculated the cost based on the used quotas (with the quotasfrom the remainder deducted). This may happen during the session. Areverse calculation is performed in step 604 to calculate the quotasthat the cost would be give the user i.e. charged quotas. In step 605deducting the charged quotas from the used quotas to get the unusedquotas or remainder are done. If the remainder is above 0 then theresult is to be stored in a specific account in step 606. In step 607 itis selected and setup rules for using the remainder based on the type ofsession e.g. data or voice, location restriction, time restrictions. Instep 608 it is selected or created a remainder account with a matchingrestriction. Step 609 stores the remainder and set the StateTimer on theremainder account.

FIG. 7 is a block diagram showing an exemplary computing device forimplementing a charging control node for controlling a present servicecharging session for charging service usage in a communication networkin the form of computing system environment 700.

Although as made clear above, the computing system environment 700 isonly one example of a suitable computing environment for an OCS and isnot intended to suggest any limitation as to the scope of use orfunctionality of the claimed subject matter. Further, the computingenvironment 700 is not intended to suggest any dependency or requirementrelating to the claimed subject matter and any one or combination ofcomponents illustrated in the example operating environment 700.

An example of a device for implementing the previously describedinnovation includes a general purpose computing device in the form of acomputer 710. Components of computer 710 can include, but are notlimited to, a processing unit 720, a system memory 730, and a system bus721 that couples various system components including the system memoryto the processing unit 720. The system bus 721 can be any of severaltypes of bus structures including a memory bus or memory controller, aperipheral bus, and a local bus using any of a variety of busarchitectures.

Computer 710 can include a variety of computer readable media. Computerreadable media can be any available media that can be accessed bycomputer 710. By way of example, and not limitation, computer readablemedia can comprise computer storage media and communication media.Computer storage media includes volatile and nonvolatile as well asremovable and non-removable media implemented in any method ortechnology for storage of information such as computer readableinstructions, data structures, program modules or other data. Computerstorage media includes, but is not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, CDROM, digital versatile disks (DVD)or other optical disk storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium which can be used to store the desired information and which canbe accessed by computer 710. Communication media can embody computerreadable instructions, data structures, program modules or other data ina modulated data signal such as a carrier wave or other transportmechanism and can include any suitable information delivery media.

The system memory 730 can include computer storage media in the form ofvolatile and/or nonvolatile memory such as read only memory (ROM) and/orrandom access memory (RAM). A basic input/output system (BIOS),containing the basic routines that help to transfer information betweenelements within computer 710, such as during start-up, can be stored inmemory 730. Memory 730 can also contain data and/or program modules thatare immediately accessible to and/or presently being operated on byprocessing unit 720. By way of non-limiting example, memory 730 can alsoinclude an operating system, application programs, other programmodules, and program data.

In one embodiment the Interface Unit 790 is a software module loaded inthe memory and processable by the processing unit, adapting the chargingcontrol node for receiving a first request for grant of a reservationservice unit quota from a charging client, the first request includingat least data identifying an account to charge for the service usage.The Determination Unit 780 is a software module loaded in the memory andprocessable by the processing unit adapting the charging control nodefor: determining a first granted service unit quota for the firstrequest; accessing a first carry-over service unit quota from a previousservice charging session associated with the identified account;determining a first reservation service unit quota by deducting thefirst carry-over service unit quota from the first granted service unitquota; reserving for the first reservation service unit quota from theaccount. The interface unit software module is further adapting thecharging control node for sending the first granted service unit quotato the charging client and receiving a clearing request from thecharging client including data enabling a first used amount of serviceunits to be determined. The determination unit is further adapting thecharging control node for determining an outstanding service unit quotaby deducting the first carryover service unit quota from the first usedamount of service unit and deducting for the outstanding service unitquota from the account.

The computer 710 can also include other removable/non-removable andvolatile/nonvolatile computer storage media. For example, computer 710can include a hard disk drive that reads from or writes tonon-removable, nonvolatile magnetic media, a magnetic disk drive thatreads from or writes to a removable, nonvolatile magnetic disk, and/oran optical disk drive that reads from or writes to a removable,nonvolatile optical disk, such as a CD-ROM or other optical media. Otherremovable/non-removable, volatile/nonvolatile computer storage mediathat can be used in the exemplary operating environment include, but arenot limited to, magnetic tape cassettes, flash memory cards, digitalversatile disks, digital video tape, solid state RAM, solid state ROMand the like. A hard disk drive can be connected to the system bus 721through a non-removable memory interface such as an interface, and amagnetic disk drive or optical disk drive can be connected to the systembus 721 by a removable memory interface, such as an interface.

A user can enter commands and information into the computer 710 throughinput devices such as a keyboard or a pointing device such as a mouse,trackball, touch pad, and/or other pointing device. Other input devicescan include a microphone, joystick, game pad, satellite dish, scanner,or similar devices. These and/or other input devices can be connected tothe processing unit 720 through user input 740 and associatedinterface(s) that are coupled to the system bus 721, but can beconnected by other interface and bus structures, such as a parallelport, game port or a universal serial bus (USB).

A graphics subsystem can also be connected to the system bus 721. Inaddition, a monitor or other type of display device can be connected tothe system bus 721 through an interface, such as output interface 750,which can in turn communicate with video memory. In addition to amonitor, computers can also include other peripheral output devices,such as speakers and/or printing devices, which can also be connectedthrough output interface 750.

The computer 710 can operate in a networked or distributed environmentusing logical connections to one or more other remote computers, such asremote server 770, which can in turn have media capabilities differentfrom device 710. The remote server 770 can be a personal computer, aserver, a router, a network PC, a peer device or other common networknode, and/or any other remote media consumption or transmission device,and can include any or all of the elements described above relative tothe computer 710. The logical connections depicted in FIG. 7 include anetwork 771, such as a local area network (LAN) or a wide area network(WAN), but can also include other networks/buses.

When used in a LAN networking environment, the computer 710 is connectedto the LAN 771 through a network interface or adapter. When used in aWAN networking environment, the computer 710 can include acommunications component, such as a modem, or other means forestablishing communications over a WAN, such as the Internet. Acommunications component, such as a modem, which can be internal orexternal, can be connected to the system bus 721 through the user inputinterface at input 740 and/or other appropriate mechanism.

In a networked environment, program modules depicted relative to thecomputer 710, or portions thereof, can be stored in a remote memorystorage device. It should be noted that the network connections shownand described are exemplary and other means of establishing acommunications link between the computers can be used.

Additionally, it should be noted that as used in this application, termssuch as “component,” “display,” “interface,” and other similar terms areintended to refer to a computing device, either hardware, a combinationof hardware and software, software, or software in execution as appliedto a computing device. For example, a component may be, but is notlimited to being, a process running on a processor, a processor, anobject, an executable, a thread of execution, a program and a computingdevice. As an example, both an application running on a computing deviceand the computing device can be components. One or more components canreside within a process and/or thread of execution and a component canbe localized on one computing device and/or distributed between two ormore computing devices, and/or communicatively connected modules.Further, it should be noted that as used in this application, terms suchas “system user,” “user,” and similar terms are intended to refer to theperson operating the computing device referenced above.

When an element is referred to as being “connected”, “coupled”,“responsive”, or variants thereof to another element, it can be directlyconnected, coupled, or responsive to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected”, “directly coupled”, “directly responsive”,or variants thereof to another element, there are no interveningelements present. Like numbers refer to like elements throughout.Furthermore, “coupled”, “connected”, “responsive”, or variants thereofas used herein may include wirelessly coupled, connected, or responsive.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Well-known functions or constructions may not be described indetail for brevity and/or clarity. The term “and/or” includes any andall combinations of one or more of the associated listed items.

As used herein, the terms “comprise”, “comprising”, “comprises”,“include”, “including”, “includes”, “have”, “has”, “having”, or variantsthereof are open-ended, and include one or more stated features,integers, elements, steps, components or functions but does not precludethe presence or addition of one or more other features, integers,elements, steps, components, functions or groups thereof. Furthermore,as used herein, the common abbreviation “e.g.”, which derives from theLatin phrase “exempli gratia,” may be used to introduce or specify ageneral example or examples of a previously mentioned item, and is notintended to be limiting of such item. The common abbreviation “i.e.”,which derives from the Latin phrase “id est,” may be used to specify aparticular item from a more general recitation.

It should also be noted that in some alternate implementations, thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved. Moreover, the functionality of a given block of the flowchartsand/or block diagrams may be separated into multiple blocks and/or thefunctionality of two or more blocks of the flowcharts and/or blockdiagrams may be at least partially integrated.

Finally, other blocks may be added/inserted between the blocks that areillustrated. Moreover, although some of the diagrams include arrows oncommunication paths to show a primary direction of communication, it isto be understood that communication may occur in the opposite directionto the depicted arrows.

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and sub-combination of these embodiments.Accordingly, the present specification, including the drawings, shall beconstrued to constitute a complete written description of variousexemplary combinations and sub-combinations of embodiments and of themanner and process of making and using them, and shall support claims toany such combination or sub-combination.

Many variations and modifications can be made to the embodiments withoutsubstantially departing from the principles of the present invention.All such variations and modifications are intended to be included hereinwithin the scope of the present invention.

The before mentioned excess-charging will be removed by remembering theusage between the service charging sessions within the same chargingsession or between charging sessions.

The remembered, i.e. stored, usage is accessible by the OCS and usedwithin a subsequent service charging session or charging session.

For example a subscriber is charged 1.50

/minute for every started minute. The user then talks for 1.5 minutesthis would result in a remainder of 30 seconds. A calculation would givefor example that the cost for the 1 minute is 1.50+cost for the 0.5minute i.e. 1.50 gives a total cost of 3

. Taking 3/1.50 gives 2 minutes and the remainder (or unused quota) isthen 2−1.5 which is 0.5 minutes or 30 seconds.

The unused quota may have a rule associated with them so that quota thatis for example for international calls cannot be used for national callsetc.

Several types of entity relationships are possible. A user may have aplurality of accounts as well as a plurality of carry-over service unitsbalances associated with it. A carry-over service unit's balance mayhave a plurality of usage rules associated with it.

The total usage for all service sessions for one service during thecharging session is considered. The charged but not used units arededucted from the usage for next service session for that service. Thisis done by having a surviving service state for the total chargingsession that survives the termination of the service session. In thiscontinues session state the total usage and charged usage may beincluded.

The surviving session state is for one unique charging session to beable to support parallel charging sessions without interference betweenthe charging sessions.

1-21. (canceled)
 22. A method performed by a charging control node forcontrolling a present service charging session for charging serviceusage in a communication network, said method comprising the steps of:receiving a first request for grant of a reservation service unit quotafrom a charging client, the first request including at least dataidentifying an account to charge for the service usage; determining afirst granted service unit quota for the first request; accessing afirst carry-over service unit quota from a previous service chargingsession associated with the identified account; determining a firstreservation service unit quota by deducting the first carry-over serviceunit quota from the first granted service unit quota; reserving for thefirst reservation service unit quota from the account; sending the firstgranted service unit quota to the charging client; receiving a clearingrequest from the charging client including data enabling a first usedamount of service units to be determined; determining an outstandingservice unit quota by deducting the first carry-over service unit quotafrom the first used amount of service unit; and deducting for theoutstanding service unit quota from the account.
 23. The methodaccording to claim 22, wherein the method includes, before the step ofreceiving the first request for grant of a service unit quota, thefurther steps of: receiving a second request for grant of a reservationservice unit quota from the charging client, the second requestincluding at least data identifying an account to charge for the serviceusage; determining a second reservation service unit quota for thesecond request; reserving for the second reservation service unit quotafrom the account; sending the second reservation service unit quota tothe charging client; receiving a service usage termination messageincluding data enabling a second used amount of service units to bedetermined; determining a second charged amount of service units byrounding up the first used amount of service units to a predefinedresolution of service units; deducting for the second charged amount ofservice units from the account; and storing data in association with theaccount such that the first carry-over service units quota based ondifference between the second charged amount of service units and thesecond used amount of service units can be determined.
 24. The methodaccording to claim 23, wherein the step of storing data in associationwith the account includes determining a rule for accessing the firstcarry-over service units quota and where the step of accessing furtherincludes accessing the first carry-over service units quota inaccordance with the rule.
 25. The method according to claim 24, whereinthe rule includes a timer and where the step of accessing in accordancewith said rule includes accessing only if the timer is unexpired. 26.The method according to claim 22, wherein the method includes, after thestep of deducting for the outstanding service unit quota, the furtherstep of: determining and storing data in association with the accountsuch that a second carry-over service units quota based on differencebetween the outstanding service unit quota and the amount of serviceunits deducted for can be determined.
 27. The method according to claim22, wherein sending the first granted service unit quota to the chargingclient includes sending a quota holding time parameter and wherein theclearing request is received following a quota holding time expiry. 28.The method according to claim 22, wherein the service charging sessionis an Internet Engineering Task Force Multiple Services Credit Control.29. The method according to claim 22, wherein the present servicecharging session and the previous service charging session relate toseparate charging sessions.
 30. The method according to claim 22,wherein the service usage comprises a data service usage including atleast one of a data bearer, IP bearer, IP flow, service data flow, or avoice call.
 31. A charging control node for controlling a presentservice charging session for charging service usage in a communicationnetwork comprising: an interface unit configured to receive a firstrequest for grant of a reservation service unit quota from a chargingclient, the first request including at least data identifying an accountto charge for the service usage; a determination unit configured to:determine a first granted service unit quota for the first request;access a first carry-over service unit quota from a previous servicecharging session associated with the identified account; determine afirst reservation service unit quota by deducting the first carry-overservice unit quota from the first granted service unit quota; andreserve for the first reservation service unit quota from the account;wherein the interface unit is further configured to: send the firstgranted service unit quota to the charging client; receive a clearingrequest from the charging client including data enabling a first usedamount of service units to be determined; and wherein the determinationunit is further configured to: determine an outstanding service unitquota by deducting the first carry-over service unit quota from thefirst used amount of service unit; and deduct for the outstandingservice unit quota from the account.
 32. The charging control nodeaccording to claim 31, wherein, in response to receiving a secondrequest for grant of a reservation service unit from the chargingclient, said second request including at least data identifying anaccount to charge for the service and being received via the interfaceunit in advance of the first request, the determining unit is configuredto: determine a second reservation service unit quota for the secondrequest, and reserve for the second reservation service unit quota fromthe account; send the second reservation service unit quota to thecharging client; receive a service usage termination message includingdata enabling a second used amount of service units to be determined;determine a second charged amount of service units by rounding up thefirst used amount of service units to a predefined resolution of serviceunits; deduct for the second charged amount of service units from theaccount; and store data in association with the account such that thefirst carry-over service units quota can be determined based on adifference between the second charged amount of service units and thesecond used amount of service units.
 33. The charging control nodeaccording to claim 32, wherein the determining unit is configured todetermine a rule for accessing the first carry-over service units quota,and to access the first carry-over service units quota in accordancewith the rule.
 34. The charging control node according to claim 31,wherein, after deducting for the outstanding service unit quota, thedetermining unit is configured to determine and store data inassociation with the account such that a second carry-over service unitsquota can be determined based on a difference between the outstandingservice unit quota and the amount of service units deducted.
 35. Thecharging control node according to claim 31, wherein the servicecharging session is an Internet Engineering Task Force Multiple ServicesCredit Control.
 36. The charging control node according to claim 31,wherein the present service charging session and the previous servicecharging session relate to separate charging sessions.
 37. Anon-transitory computer-readable medium storing a computer programcomprising instructions that, when executed by a processor in a chargingcontrol node, causes the charging control node to control a presentservice charging session for charging service usage in a communicationnetwork, based on the computer program including program instructionscausing the charging control node to: receive a first request for grantof a reservation service unit quota from a charging client, the firstrequest message including at least data identifying an account to chargefor the service usage; determine a first granted service unit quota forthe first request; access a first carry-over service unit quota from aprevious service charging session associated with the identifiedaccount; determine a first reservation service unit quota by deductingthe first carry-over service unit quota from the first granted serviceunit quota; reserve for the first reservation service unit quota fromthe account; send the first granted service unit quota to the chargingclient; receive a clearing request from the charging client includingdata enabling a first used amount of service units to be determined;determine an outstanding service unit quota by deducting the firstcarry-over service unit quota from the first used amount of serviceunit; and deduct for the outstanding service unit quota from theaccount.
 38. The non-transistory computer-readable medium of claim 37,wherein the computer program further includes instructions that, inresponse to the charging control node receiving a second request forgrant of a reservation service unit quota from the charging client inadvance of receiving the first request for grant of a service unitquota, configure the charging control node to: determine a secondreservation service unit quota for the second request, wherein thesecond request including at least data identifying an account to chargefor the service usage; reserve for the second reservation service unitquota from the account; send the second reservation service unit quotato the charging client; receive a service usage termination messageincluding data enabling a second used amount of service units to bedetermined; determine a second charged amount of service units byrounding up the first used amount of service units to a predefinedresolution of service units; and deduct for the second charged amount ofservice units from the account: store data in association with theaccount such that the first carry-over service units quota based ondifference between the second charged amount of service units and thesecond used amount of service units can be determined.
 39. Thenon-transistory computer-readable medium according to claim 38, whereinthe computer program further comprises program instructions that, whenexecuted by the processor of the charging control node, causes thecharging control node to determine a rule for accessing the firstcarry-over service units quota and to access the first carry-overservice units quota in accordance with said rules.
 40. Thenon-transistory computer-readable medium according to claim 37, whereinthe computer program further comprises program instructions that, whenexecuted by the processor of the charging control node, causes thecharging control node to, after deducting for the outstanding serviceunit quota, determine and store data in association with the account sothat a second carry-over service units quota can be determined based ona difference between the outstanding service unit quota and the amountof service units deducted.
 41. The non-transistory computer-readablemedium according to claim 37, wherein the computer program furthercomprises program instructions that, when executed by the processor ofthe charging control node, causes the charging control node to, afterdeducting for the outstanding service unit quota, send and receive usingInternet Engineering Task Force Multiple Services Credit Control.